Method for Synchronizing Pdcp Operations After Rrc Connection Re-Establishment in a Wireless Communication System and Related Apparatus Thereof

1. A method for synchronizing Packet Data Convergence Protocol (PDCP) operations in a wireless communication system, the method comprising: when an radio resource control (RRC) connection is re-established, performing an RRC reconfiguration procedure to resume all radio bearers other than a signaling radio bearer 1 (SRB 1 ); when a data radio bearer (DRB) mapped on Radio Link Control (RLC) Acknowledged Mode (AM) is resumed, transmitting PDCP Service Data Units (SDUs) or receiving PDCP SDUs after resetting state variables of a PDCP sequence number of a next PDCP SDU (Next_PDCP_TX_SN), a HFN value for generation of a count value used for PDCP Packet Data Units (TX_HFN), a next expected PDCP sequence number by a receiving PDCP entity (Next_PDCP_RX_SN) and a HFN value for generation of a count value used for received PDCP Packet Data Units (RX_HFN) to initial values.

2. The method of claim 1 , wherein the DRB comprises an SRB 2 .

3. A method for synchronizing Packet Data Convergence Protocol (PDCP) operations in a wireless communication system, the method comprising: when an RRC connection is re-established, performing an RRC reconfiguration procedure to resume all radio bearers other than a signaling radio bearer 1 (SRB 1 ); when a data radio bearer (DRB) mapped on Radio Link Control (RLC) Acknowledged Mode (AM) is resumed, receiving PDCP Service Data Units (SDUs); starting a timer to reorder the PDCP SDUs to generate received in-sequence PDCP SDUs; and when the timer expires, performing a header decompression on the received in-sequence PDCP SDUs.

4. The method of claim 3 , wherein the PDCP SDUs comprises the PDCP SDUs have not been successfully received.

5. The method of claim 3 , further comprising: when the DRB is resumed, transmitting a PDCP status report, wherein the PDCP SDUs comprises PDCP SDUs negatively acknowledged in the PDCP status report.

6. The method of claim 3 , wherein the DRB comprises an SRB 2 .

7. A communication device for synchronizing Packet Data Convergence Protocol (PDCP) operations with another communication device, the communication device comprises: means for performing an RRC Reconfiguration procedure to resume all radio bearers other than a signaling radio bearer 1 (SRB 1 ) when an RRC connection is re-established; means for transmitting PDCP Service Data Units (SDUs) or receiving PDCP SDUs after resetting state variables of a PDCP sequence number of a next PDCP SDU (Next_PDCP_TX_SN) and a HFN value for generation of a count value used for PDCP Packet Data Units (TX_HFN), a next expected PDCP sequence number by a receiving PDCP entity (Next_PDCP_RX_SN) and a HFN value for generation of a count value used for received PDCP Packet Data Units (RX_HFN) to initial values when a data radio bearer (DRB) mapped on Radio Link Control (RLC) Acknowledged Mode (AM) is resumed.

8. The communication device of claim 7 , wherein the communication device is an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), and the other communication device is a user equipment (UE); or the communication device is a UE, and the other communication device is an E-UTRAN.

9. The E-UTRAN of claim 7 , wherein the DRB comprises an SRB 2 .

10. A communication device for synchronizing Packet Data Convergence Protocol (PDCP) operations with another communication device, the communication device comprises: means for performing an RRC reconfiguration procedure to resume all radio bearers other than a SRB 1 when an RRC connection is re-established; means for receiving PDCP Service Data Units (SDUs) when a data radio bearer (DRB) mapped on Radio Link Control (RLC) Acknowledged Mode (AM) is resumed; means for starting a timer to reorder the PDCP SDUs to generate received in-sequence PDCP SDUs; and means for performing a header decompression on the received in-sequence PDCP SDUs when the timer expires.

11. The communication device of claim 10 , wherein the PDCP SDUs comprises the PDCP SDUs have not been successfully received by the communication device.

12. The communication device of claim 10 , further comprising means for transmitting a PDCP status report, wherein the PDCP SDUs comprises the PDCP SDUs negatively acknowledged in the PDCP status report.

13. The communication device of claim 10 , wherein the communication device is an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), and the other communication device is a user equipment (UE); or the communication device is a UE, and the other communication device is an E-UTRAN.

14. The communication device of claim 10 , wherein the DRB comprises an SRB 2 .